Field effect transistors and methods of forming same

ABSTRACT

Semiconductor devices and methods of forming the same are provided. A semiconductor device includes a substrate, the substrate having a first source/drain feature and a second source/drain feature formed thereon. The semiconductor device further includes a first nanowire on the first source/drain feature and a second nanowire on the second source/drain feature, the first nanowire extending vertically from an upper surface of the first source/drain feature and the second nanowire extending vertically from an upper surface of the second source/drain feature. The semiconductor device further includes a third nanowire extending from an upper end of the first nanowire to an upper end of the second nanowire, wherein the first nanowire, the second nanowire and the third nanowire form a channel.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a divisional of U.S. application Ser. No.14/675,333, filed on Mar. 31, 2015, entitled “Field Effect Transistorsand Methods of Forming Same,” which application is hereby incorporatedherein by reference in its entirety.

BACKGROUND

Transistors are key components of modern integrated circuits. To satisfythe requirements of increasingly faster switching speed, the drivecurrents of transistors need to be increasingly higher. At the sametime, the gate lengths of transistors are constantly being scaled down.Scaling down the gate lengths leads to undesirable effects known as“short-channel effects,” with which the control of current flow by thegates is compromised. Among the short-channel effects are thedrain-induced barrier lowering (DIBL) and the degradation ofsub-threshold slope, both of which result in the degradation in theperformance of transistors.

The use of multi-gate transistor architecture may help the relief ofshort-channel effects by improving electrostatic control of the gate onthe channel. Fin field-effect transistors (FinFET) were thus developed.To further increase the control of the channels, and to reduce theshort-channel effects, transistors having gate-all-around (GAA)structures were also developed, wherein the respective transistors arealso referred to as gate all around transistors. In a gate all aroundtransistor, a gate dielectric and a gate electrode fully encircle thechannel region. This configuration delivers a good control of thechannel, and the short-channel effects are reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1A-13B illustrate various top and cross-sectional views of afabrication process of a semiconductor device in accordance with someembodiments.

FIG. 14 is a flow diagram illustrating a method of forming asemiconductor device in accordance with some embodiments.

FIGS. 15A-24B illustrate various top and cross-sectional views of afabrication process of a semiconductor device in accordance with someembodiments.

FIG. 25 is a flow diagram illustrating a method of forming asemiconductor device in accordance with some embodiments.

FIGS. 26A-33B illustrate various top and cross-sectional views of afabrication process of a semiconductor device in accordance with someembodiments.

FIG. 34 is a flow diagram illustrating a method of forming asemiconductor device in accordance with some embodiments.

FIGS. 35A-42B illustrate various top and cross-sectional views of afabrication process of a semiconductor device in accordance with someembodiments.

FIG. 43 is a flow diagram illustrating a method of forming asemiconductor device in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Field effect transistors (FETs) and methods of forming the same areprovided in accordance with various exemplary embodiments. Theintermediate stages of forming the FETs are illustrated. Variations ofthe embodiments are discussed. Throughout the various views andillustrative embodiments, like reference numbers are used to designatelike elements.

Embodiments such as those described herein provide FETs with one or morechannels formed of vertical and horizontal nanowires. Hence, thechannels have vertical and horizontal portions. The use of the nanowiresallows for forming FETs in a gate-all-around (GAA) configuration, wheregate stacks wrap around the channels for improved gate control. SuchFETs may be also referred to as GAA FETs. Furthermore, the use verticaland horizontal nanowires allows for formation of FETs having differentgate lengths that are defined by a single patterning step.

FIGS. 1A-13B illustrate various intermediate stages of fabrication of asemiconductor device 100 in accordance with some embodiments. FIGS.1A-13B illustrate top and cross-sectional views, wherein an “A” figurerepresents a top view and a “B” figure represents a cross-sectional viewalong the B-B′ line of the respective “A” figure.

Referring first to FIGS. 1A and 1B, a portion of a substrate 101 havinga first feature 103 and a second feature 105 formed thereon isillustrated. The substrate 101 may be formed of silicon, although it mayalso be formed of other group III, group IV, and/or group V elements,such as germanium, gallium, arsenic, and combinations thereof. Thesubstrate 101 may also be in the form of silicon-on-insulator (SOI).Generally, an SOI substrate comprises a layer of a semiconductormaterial (e.g., silicon, germanium and/or the like) formed on aninsulator layer. The insulator layer may be, for example, a buried oxide(BOX) layer or a silicon oxide layer. In addition, other substrates thatmay be used include multi-layered substrates, gradient substrates,hybrid orientation substrates, any combinations thereof and/or the like.As described below in greater detail, in some embodiments, portions ofthe substrate 101 are implanted with p-type impurities (such as boron orindium) or n-type impurities (such as phosphorous, arsenic, orantimony). The implanted regions have reduced resistivity, and hence mayact as source/drain regions for subsequently formed devices, such as,for example, FETs.

In some embodiments, the substrate 101 is patterned to form the firstfeature 103 and the second feature 105. The substrate 101 may bepatterned using suitable lithography and etch techniques. In someembodiments, a photoresist material (not shown) is formed over thesubstrate 101, which is then masked, exposed, and developed. After thephotoresist material is patterned, an etch processes may be performed toremove unwanted portions of the underlying substrate 101. Additionalmasks (not shown), for example, hard masks, may be utilized during theetch process. Subsequently, the photoresist material may be removedusing, for example, an ashing process combined with a wet clean process.In an embodiment where the substrate 101 comprises silicon, thesubstrate 101 may be anisotropically etched using, for example, a dryplasma etch with etchant gases such as Cl₂, HBr, CF₄, SF₆, NF₃, and thelike. As described below in greater detail, the first feature 103 andthe second feature 105 are doped using suitable dopants and act as afirst source/drain feature 103 and a second source/drain feature 105,respectively, for the semiconductor device 100.

Referring further to FIGS. 1A and 1B, in the illustrated embodiment, thefirst feature 103 and the second feature 105 are formed by patterningthe substrate 101 and, accordingly, comprise a same material as thesubstrate 101. In other embodiments, the first feature 103 and thesecond feature 105 may be formed on the substrate using, for example, anepitaxial growth process. In such embodiments, the first feature 103 andthe second feature 105 may comprise a material that is different fromthe substrate 101.

Referring to FIGS. 2A and 2B, a shallow trench isolation (STI) structure201 is formed over the substrate 101 and surrounding the first feature103 and the second feature 105. In some embodiments, the STI structure201 may comprise a dielectric material such as, for example, siliconoxide, silicon nitride, silicon oxynitride, fluoride-doped silicateglass (FSG), low-k dielectrics such as carbon doped oxides, extremelylow-k dielectrics such as porous carbon doped silicon oxide, a polymersuch as polyimide, combinations of these, or the like. In someembodiments, the STI structure 201 may be formed using, for example,chemical vapor deposition (CVD), a spin-on process, a thermal oxidationprocess, although any other acceptable process may be also utilized. Insome embodiments, a dielectric material of the STI structure 201 isformed over the substrate 101. Subsequently, portions of the dielectricmaterial extending over top surfaces of the first feature 103 and thesecond feature 105 are removed to expose the top surfaces of the firstfeature 103 and the second feature 105 such that the top surfaces of thefirst feature 103 and the second feature 105 are substantially coplanarwith a top surface of the STI structure 201. In some embodiments, excessportions of the dielectric material may be removed using, for example,an etch process, a grinding process, a chemical mechanical polishing(CMP) process, and the like.

In some embodiments, the first feature 103 and the second feature 105are doped to form the first source/drain feature 103 and the secondsource/drain feature 105, respectively, of the semiconductor device 100.In some embodiments wherein the semiconductor device 100 is an n-typeFET (NFET) and the substrate 101 comprises silicon, the first feature103 and the second feature 105 may be n-doped using, for example,phosphorus (P), or arsenic (As). In some embodiments wherein thesemiconductor device 100 is a p-type FET (PFET) and the substrate 101comprises silicon, the first feature 103 and the second feature 105 maybe p-doped using, for example, boron (B). In some embodiments, the firstfeature 103 and the second feature 105 may be doped using an ionimplantation method, or the like. In some embodiments wherein the firstfeature 103 and the second feature 105 are formed of an epitaxiallygrown material, the first feature 103 and the second feature 105 may bein situ doped during the epitaxial growth process.

Referring to FIGS. 3A and 3B, a dielectric layer 301 is formed over theSTI structure 201, the first source/drain feature 103, and the secondsource/drain feature 105. In some embodiments, the dielectric layer 301may comprise silicon nitride, silicon oxide, aluminum oxide, siliconcarbide, silicon oxynitride, or the like, and may be formed using, forexample, CVD, plasma-enhanced CVD (PECVD), low-pressure LPCVD, a thermaloxidation method, and the like.

In some embodiments, the dielectric layer 301 is patterned using, forexample, suitable lithography and etch processes to form a first opening303 and a second opening 305 therein. The first opening 303 exposes thefirst source/drain feature 103 and the second opening 305 exposes thesecond source/drain feature 105 as illustrated in FIGS. 3A and 3B. Inthe illustrated embodiment, top-view shapes of the first opening 303 andthe second opening 305 are circles. However, in other embodiments, thetop-view shapes of the first opening 303 and the second opening 305 maybe polygons such as triangles, rectangles, hexagons, or the like. Insome embodiments, the first opening 303 and the second opening 305 havea same lateral dimension D₁ between about 2 nm and about 50 nm. Asdescribed below in greater detail, vertical nanowires (see FIGS. 4A and4B) are formed in the first opening 303 and the second opening 305 andthe dielectric layer 301 acts as a template layer for nanowireformation. Accordingly, the dielectric layer 301 may also be referred toas a template layer 301. Moreover, widths of the subsequently formednanowires may be controlled by lateral dimensions of the openings. Insome embodiments, widths of the nanowires may equal to the lateraldimensions of corresponding openings.

Referring further to FIGS. 3A and 3B, in the illustrated embodiment, asingle pair of openings (such as the first opening 303 and the secondopening 305) is formed in the template layer 301. However, one havingordinary skill in the art would appreciate that more than a single pairof openings may be formed in the template layer 301 depending on anumber of semiconductor devices (such as the semiconductor device 100)that are subsequently formed on the substrate 101. As described below ingreater detail, a distance between a pair of openings (such as the firstopening 303 and the second opening 305) determines a channel length ofthe subsequently formed semiconductor device (such as the semiconductordevice 100). Accordingly, by forming a plurality of opening pairs havingdifferent distances between openings, semiconductor devices of differentchannel lengths may be formed. In some embodiments, the plurality ofopening pairs may be formed using a single patterning process.Accordingly, the channel lengths of the semiconductor devices may beadvantageously controlled by a single patterning process. In someembodiment, a distance D₂ between the first opening 303 and the secondopening 305 is between about 5 nm and about 100 nm.

Referring to FIGS. 4A and 4B, a first nanowire 401 and a second nanowire403 are formed in the first opening 303 and the second opening 305,respectively. As described below in greater detail, the first nanowire401 and the second nanowire 403 form vertical portions of a channel ofthe semiconductor device 100. In some embodiments, the first nanowire401 and the second nanowire 403 may comprise III-V compoundsemiconductor materials, and may be epitaxial grown using, for example,a selective-area Metal-Organic Chemical Vapor Deposition (MOCVD).Typical group III materials may include gallium (Ga), indium (In), andaluminum (Al), and suitable precursors thereof may include trimethylindium (TMIn), triethyl gallium (TEGa), trimethyl gallium (TMGa),trimethyl aluminum (TMAl), tritertiarybutyl aluminum (TTBAl), or thelike. Typical group V materials may include arsenic (As), antimony (Sb),phosphorus (P), and bismuth (Bi), and suitable precursors thereof mayinclude tributyl arsenic (TBA), arsine (AsH₃), phosphine (PH₃), tributylphosphorus (TBP), trimethyl antimony (TMSb), triethyl antimony (TESb),triphenyl bismuth (TPB), or the like.

In some embodiments, process parameters of the epitaxial growth processmay be adjusted such that the first nanowire 401 and the second nanowire403 predominantly grow in a vertical direction (a directionsubstantially perpendicular to the top surfaces of the firstsource/drain feature 103 and the second source/drain feature) whilemaintaining widths determined by the lateral dimension D₁ of the firstopening 303 and the second opening 305. Accordingly, the lateraldimension D₁ of the first opening 303 and the second opening 305controls widths of the first nanowire 401 and the second nanowire 403.In some embodiments, lengths of the first nanowire 401 and the secondnanowire 403 are controlled by a duration of the epitaxial growthprocess. In some embodiments wherein the first nanowire 401 and thesecond nanowire 403 are formed by a same epitaxial growth process,lengths of the first nanowire 401 and the second nanowire 403 may besubstantially the same. In some embodiments, a length L₁ of the firstnanowire 401 and the second nanowire 403 is between about 5 nm and about5 μm.

Referring to FIGS. 5A through 6B, a first portion of a gate stackcomprising a gate dielectric layer 501 and a work function layer 503 isformed wrapping the first nanowire 401 and the second nanowire 403.Turning first to FIGS. 5A and 5B, the gate dielectric layer 501 isformed over the template layer 301 and top surfaces and sidewalls of thefirst nanowire 401 and the second nanowire 403. In some embodiments, thegate dielectric layer 501 comprises one or more layers of high-kdielectric materials. Generally, a high-k dielectric material has adielectric constant (k-value) higher than 3.9. For example, the gatedielectric layer 501 may include one or more layers of a metal oxide ora silicate of Hf, Al, Zr, combinations thereof, or multi-layers thereof.Other suitable materials may include La, Mg, Ba, Ti, Pb in the form ofmetal oxides, metal alloyed oxides, or combinations thereof. In someembodiments, the gate dielectric layer 501 may be formed using atomiclayer deposition (ALD), CVD, PECVD, molecular-beam deposition (MBD), orthe like.

Referring further to FIGS. 5A and 5B, in some embodiments the workfunction layer 503 is formed over the gate dielectric layer 501. Thework function layer 503 may be used to adjust a work function of asubsequently formed gate electrode layer to exhibit the work functionsuitable to a particular type of the semiconductor device 100 such as,for example, an NFET or a PFET. In some embodiments wherein thesemiconductor device 100 is an NFET, the work function layer 503 maycomprise one or more layers of, for example, Ti, Ag, Al, TiAl, TiAlN,TiAlC, TaC, TaCN, TaSiN, TaAlC, Mn, Zr, or the like. In otherembodiments wherein the semiconductor device 100 is a PFET, the workfunction layer 503 may comprise one or more layers of, for example, TiN,WN, TaN, Ru, Co, or the like. In some embodiments the work functionlayer 503 may be formed using ALD, CVD, PECVD, MBD, or the like.

Referring to FIGS. 6A and 6B, portions of the gate dielectric layer 501and the work function layer 503 are removed such that the gatedielectric layer 501 and the work function layer 503 remain on thesidewalls of the first nanowire 401 and the second nanowire 403. Inaddition, top portions of the first nanowire 401 and the second nanowire403 are also exposed. In some embodiments, the portions of the gatedielectric layer 501 and the work function layer 503 may be removedusing, for example, a suitable anisotropic etch process.

Referring to FIGS. 7A and 7B, a dielectric layer 701 is formed over thesubstrate 101 and surrounding the first nanowire 401 and the secondnanowire 403. The dielectric layer 701 may be formed of similarcandidate materials and using similar candidate methods as the STIstructure 201 and the description is not repeated herein. Subsequently,portions of the dielectric layer 701 extending over the top surfaces ofthe first nanowire 401 and the second nanowire are removed to expose thetop surfaces of the first nanowire 401 and the second nanowire 403 suchthat the top surfaces of the first nanowire 401 and the second nanowireare substantially coplanar with a top surface of the dielectric layer701. In some embodiments, excess portions of the dielectric layer 701may be removed using, for example, an etch process, a grinding process,a CMP process, and the like.

Referring to FIGS. 8A and 8B, an opening 801 is formed in the dielectriclayer 701 to expose top portions of the first nanowire 401 and thesecond nanowire 403. In some embodiments, the dielectric layer 701 ispatterned using suitable lithography and etch processes to form theopening 801. In some embodiments, the opening 801 is formed to a depthsuch that top surfaces of the gate dielectric layer 501 and the workfunction layer 503 are exposed. In some embodiments, a width W₁ of theopening 801 is between about 2 nm and about 50 nm, and a depth D₃ of theopening 801 is between about 2 nm and about 50 nm. As described below ingreater detail, a third nanowire 901 (see FIGS. 9A and 9B) is formed inthe in the opening 801. In some embodiments, the third nanowire 901 actsas a horizontal portion of the channel of the semiconductor device 100.

Referring to FIGS. 9A and 9B, the third nanowire 901 is formed in theopening 801. In some embodiments, the third nanowire 901 forms thehorizontal portion of the channel of the semiconductor device 100. Inthe illustrated embodiment, the channel comprises the first nanowire401, the second nanowire 403, and the third nanowire 901. In someembodiments, the third nanowire 901 may be formed of similar candidatematerials (such as III-V compound semiconductor materials) as the firstnanowire 401 and the second nanowire 403 and the description is notrepeated herein. In some embodiments, the third nanowire 901 may beformed using an epitaxial growth method. In other embodiments, the thirdnanowire 901 may be formed using any suitable deposition method.Subsequently, portions of the third nanowire 901 extending over thedielectric layer 701 may be removed such that a top surface of the thirdnanowire 901 is substantially coplanar with a top surface of thedielectric layer 701. In some embodiments, excess portions of the thirdnanowire 901 may be removed using, for example, an etch process, agrinding process, a CMP process, and the like. A size of the thirdnanowire 901 is determined by a size of the opening 801 and, therefore,the third nanowire 901 may be also referred to as a lithographicallyformed nanowire, while the first nanowires 401 and the second nanowire403 may be also referred to as epitaxially formed nanowires. In theillustrated embodiment, a width of the third nanowire 901 is equal tothe width W₁ of the opening 801 and a height of the third nanowire 901is equal to the depth D₃ of the opening 801.

Referring to FIGS. 10A and 10B, a dielectric layer 1001 is formed overthe dielectric layer 701 and the third nanowire 901. In someembodiments, the dielectric layer 1001 may be formed of similarcandidate materials and using similar candidate methods as the STIstructure 201 and the description is not repeated herein. In someembodiments, the dielectric layer 701 and the dielectric layer 1001 maycomprise a same material. In other embodiments, the dielectric layer 701and the dielectric layer 1001 may comprise different materials.Subsequently, a top surface of the dielectric layer 1001 may beplanarized using, for example, a grinding process, a CMP process, andthe like.

Referring further to FIGS. 10A and 10B, an opening 1003 is formed from atop surface of the dielectric layer 1001. In some embodiments, theopening 1003 extends through the dielectric layer 1001 and into thedielectric layer 701 such that sidewalls, and top and bottom surfaces ofthe third nanowire 901 are exposed. As described below in greaterdetail, a second portion of the gate stack is formed in the opening1003. In some embodiments, the dielectric layer 1001 and the dielectriclayer 701 may be patterned using suitable lithography and etchprocesses. In some embodiments wherein the dielectric layer 701 and thedielectric layer 1001 comprise a same material, the dielectric layer 701and the dielectric layer 1001 may be selectively etched using a singleetch process. In other embodiments wherein the dielectric layer 701 andthe dielectric layer 1001 comprise different materials, the dielectriclayer 701 and the dielectric layer 1001 may be selectively etched usingmultiple etch process (for example, two etch processes).

Referring to FIGS. 11A and 11B, a second portion of the gate stackcomprising a gate dielectric layer 1101, a work function layer 1103 andgate electrode 1105 is formed in the opening 1003. In the illustratedembodiment, the second portion of the gate stack wraps around the thirdnanowire 901. In some embodiments, the gate dielectric layer 1101 isconformally formed on sidewalls and a bottom of the opening 1003, and onexposed surfaces of the third nanowire 901. In some embodiments, thegate dielectric layer 1101 is formed using similar materials and methodsas the gate dielectric layer 501 and the description is not repeatedherein. Subsequently, the work function layer 1103 is conformally formedon the gate dielectric layer 1101. In some embodiments, the workfunction layer 1103 is formed using similar materials and methods as thework function layer 503 and the description is not repeated herein.

Referring further to FIGS. 11A and 11B, the gate electrode 1105 isformed on exposed surfaces of the work function layer 1103. In someembodiments, the gate dielectric layer 1101 and the work function layer1103 do not completely fill the opening 1003, and the remaining portionof the opening 1003 may be filled by the gate electrode 1105. In someembodiments, the gate electrode 1105 may comprise a metallic materialsuch as gold, silver, aluminum, copper, tungsten, molybdenum, nickel,titanium, or alloys thereof, and may be formed using physical vapordeposition (PVD), ALD, plating, or the like. Subsequently, portions ofthe gate dielectric layer 1101, the work function layer 1103 and thegate electrode 1105 extending over the dielectric layer 1001 may beremoved such that top surfaces of the gate dielectric layer 1101, thework function layer 1103 and the gate electrode 1105 are substantiallycoplanar with the top surface of the dielectric layer 1001. In someembodiments, excess materials may be removed using, for example, an etchprocess, a grinding process, a CMP process, and the like.

Referring to FIGS. 12A and 12B, an interlayer dielectric (ILD) layer1201 is formed over the dielectric layer 1001. In some embodiments, theILD layer 1201 is formed of one or more layers of a dielectric material,such as silicon oxide, low-k dielectrics or other suitable materials, bya suitable technique, such as CVD, ALD, spin-on, or the like. In someembodiments, the ILD layer 1201 is planarized using, for example, agrinding process, a CMP process, or the like.

Referring further to FIGS. 12A and 12B, a first opening 1203, a secondopening 1205, and a third opening 1207 are formed from a top surface ofthe ILD layer 1201. In some embodiments, the first opening 1203, thesecond opening 1205, and the third opening 1207 are formed usingsuitable lithography and etching processes. In the illustratedembodiment, the first opening 1203 extends through the ILD layer 1201,the dielectric layers 1001 and 701 and the template layer 301, andexposes the first source/drain feature 103. The second opening 1205extends through the ILD layer 1201, the dielectric layers 1001 and 701and the template layer 301, and exposes the second source/drain feature105. The third opening 1207 extends through the ILD layer 1201 andexposes the gate electrode 1105.

Referring to FIGS. 13A and 13B, a first contact plug 1301, a secondcontact plug 1303, and a third contact plug 1305 are formed in the firstopening 1203, the second opening 1205, and the third opening 1207,respectively. In some embodiments, one or more barrier/adhesion layers(not shown) are conformally formed in the first opening 1203, the secondopening 1205, and the third opening 1207. The one or morebarrier/adhesion layers protect neighboring layers (such as, forexample, the ILD layer 1201, the dielectric layers 701 and 1001, and thetemplate layer 301) from metallic diffusion. The one or morebarrier/adhesion layers may comprise titanium, titanium nitride,tantalum, tantalum nitride, or the like and may be formed using PVD,CVD, ALD, the like, or a combination thereof. In some embodiments, aseed layer (not shown) is conformally formed over the one or morebarrier/adhesion layers. The seed layer may comprise copper, titanium,nickel, gold, manganese, the like, or a combination thereof, and may beformed by ALD, PVD, the like, or a combination thereof.

Referring further to FIGS. 13A and 13B, the first contact plug 1301, thesecond contact plug 1303, and the third contact plug 1305 are formed byfilling the first opening 1203, the second opening 1205, and the thirdopening 1207, respectively, with a suitable conductive material. In someembodiments, the first contact plug 1301, the second contact plug 1303,and the third contact plug 1305 may comprise copper, a copper alloy,silver, gold, tungsten, tantalum, aluminum, and the like, and may beformed using an electro-chemical plating process, an electroless platingprocess, ALD, PVD, the like, or a combination thereof.

In some embodiments, excess materials overfilling the first opening1203, the second opening 1205, and the third opening 1207 are removedsuch that the topmost surfaces of the first contact plug 1301, thesecond contact plug 1303, and the third contact plug 1305 aresubstantially coplanar with the topmost surface of the ILD layer 1201.In some embodiments, the excess materials are removed using, forexample, a mechanical grinding process, a CMP process, an etchingprocess, the like, or a combination thereof.

Referring further to FIGS. 13A and 13B, in the illustrated embodiment,top-view shapes of the first contact plug 1301, the second contact plug1303, and the third contact plug 1305 are circles. However, in otherembodiments, the top-view shapes of the first contact plug 1301, thesecond contact plug 1303, and the third contact plug 1305 may bepolygons such as triangles, rectangles, hexagons, or the like.Furthermore, locations of the first contact plug 1301, the secondcontact plug 1303, and the third contact plug 1305, as shown in FIGS.13A and 13B, are provided as examples and are not limiting. In otherembodiments, the first contact plug 1301, the second contact plug 1303,and the third contact plug 1305 may be formed at other locations basedon design requirements for the semiconductor device 100.

In some embodiments, further manufacturing steps may be performed on thesemiconductor device 100. For example, metallization layers (not shown)may be formed over the ILD layer 1201. The metallization layers maycomprise one or more dielectric layers, and one or more conductivefeatures formed in the one or more dielectric layers. In someembodiments, the metallization layers are in electrical contact with thefirst contact plug 1301, the second contact plug 1303, and the thirdcontact plug 1305, and electrically interconnect the semiconductordevice 100 to other devices formed on the substrate 101. In someembodiments, the further manufacturing steps may also include formationof one or more redistribution layers (RDLs) over the metallizationlayers, formation of under-bump metallizations (UBMs) over the RLDs, andformation of connectors over the UBMs. Subsequently, the substrate 101may be singulated into separate dies, which may further undergo variouspackaging processes.

FIG. 14 is a flow diagram illustrating a method 1400 of forming thesemiconductor device 100 in accordance with some embodiments. The method1400 starts with step 1401, wherein a first source/drain feature (suchas first source/drain feature 103) and a second source/drain feature(such as the second source/drain feature 105) are formed on a substrate(such as the substrate 101) as described above with reference to FIGS.1A-2B. In step 1403, a first nanowire (such as the first nanowire 401)and a second nanowire (such as the second nanowire 403) are formed onthe first source/drain feature and the second source/drain feature asdescribed above with reference to FIGS. 3A-4B. In some embodiments, thefirst nanowire and the second nanowire are substantially perpendicularto top surfaces of the first source/drain feature and the secondsource/drain feature. In step 1405, a first gate stack (such as the gatedielectric layer 501 and the work function layer 503) is formed wrappingaround the first nanowire and the second nanowire as described abovewith reference to FIGS. 5A-6B. In step 1407, a third nanowire (such asthe third nanowire 901) connecting the first nanowire to the secondnanowire is formed as described with reference to FIGS. 7A-9B. In someembodiment, the third nanowire is substantially parallel to the topsurfaces of the first source/drain feature and the second source/drainfeature. In some embodiments, the first nanowire, the second nanowireand the third nanowire form a channel of the semiconductor device 100.In step 1409, a second gate stack (such as the gate dielectric layer1101, the work function layer 1103 and the gate electrode 1105) isformed wrapping around the third nanowire as described above withreference to FIGS. 10A-11B.

FIGS. 15A-24B illustrate various intermediate stages of fabrication of asemiconductor device 1500 in accordance with some embodiments. FIGS.15A-24B illustrate top and cross-sectional views, wherein an “A” figurerepresents a top view and a “B” figure represents a cross-sectional viewalong the B-B′ line of the respective “A” figure. As described abovewith reference to FIGS. 5A-11B, the first portion of the gate stack ofthe semiconductor device 100 is formed after forming the first nanowire401 and second nanowire 403, but before forming the third nanowire 901,and the second portion of the gate stack of the semiconductor device 100is formed after forming the third nanowire 901. As described below ingreater detail, a gate stack of the semiconductor device 1500 is formedduring a single step after all nanowires are formed.

Referring first to FIGS. 15A and 15B, a portion of a substrate 1501having a first feature 1503 and a second feature 1505 formed thereon isillustrated. The substrate 1501 may be formed of similar materials asthe substrate 101 (see FIGS. 1A and 1B) and the description is notrepeated herein. In some embodiments, the substrate 1501 is patterned toform the first feature 1503 and the second feature 1505. In someembodiments, the first feature 1503 and the second feature 1505 may beformed using similar methods as the first feature 103 and the secondfeature 105 (see FIGS. 1A and 1B), respectively, and the description isnot repeated herein. As described below in greater detail, the firstfeature 1503 and the second feature 1505 are doped using suitabledopants and act as a first source/drain feature 1503 and a secondsource/drain feature 1505, respectively.

Referring to FIGS. 16A and 16B, an STI structure 1601 is formed over thesubstrate 1501 and surrounding the first feature 1503 and the secondfeature 1505. In some embodiments, the STI structure 1601 may be formedusing similar material and methods as the STI structure 201 (see FIGS.2A and 2B) and the description is not repeated herein. Subsequently, thefirst feature 1503 and the second feature 1505 are doped to form thefirst source/drain feature 1503 and the second source/drain feature1505, respectively. In some embodiments, the first feature 1503 and thesecond feature 1505 may be doped using similar methods as the firstfeature 103 and the second feature 105, respectively, and thedescription is not repeated herein.

Referring to FIGS. 17A and 17B, a template layer 1701 is formed over theSTI structure 1601, the first source/drain feature 1503, and the secondsource/drain feature 1505. In some embodiments, the template layer 1701may be formed using similar materials and methods as the template layer301 (see FIGS. 3A and 3B) and the description is not repeated herein.Subsequently, the template layer 1701 is patterned form a first opening1703 and a second opening 1705 therein. The first opening 1703 exposesthe first source/drain feature 1503 and the second opening 1705 exposesthe first source/drain feature 1505 as illustrated in FIGS. 17A and 17B.In some embodiments, the first opening 1703 and the second opening 1705may be formed using similar methods as the first opening 303 and thesecond opening 305 (see FIGS. 3A and 3B) and the description is notrepeated herein.

Referring to FIGS. 18A and 18B, a first nanowire 1801 and a secondnanowire 1803 are formed in the first opening 1703 and the secondopening 1705, respectively. As described below in greater detail, thefirst nanowire 1801 and the second nanowire 1803 form vertical portionsof a channel of the semiconductor device 1500. In some embodiments, thefirst nanowire 1801 and the second nanowire 1803 may be formed usingsimilar material and methods as the first nanowire 401 and the secondnanowire 403 (see FIGS. 4A and 4B) and the description is not repeatedherein.

Referring to FIGS. 19A and 19B, a dielectric layer 1901 is formed overthe template layer 1701 and surrounding the first nanowire 1801 and thesecond nanowire 1803. In some embodiments, the dielectric layer 1901 maybe formed using similar materials and methods as the dielectric layer701 (see FIGS. 7A and 7B) and the description is not repeated herein.

Referring to FIGS. 20A and 20B, an opening 2001 is formed in thedielectric layer 1901 to expose top portions of the first nanowire 1801and the second nanowire 1803. In some embodiments, the opening 2001 maybe formed using similar methods as the opening 801 (see FIGS. 8A and 8B)and the description is not repeated herein. As described below ingreater detail, a third nanowire 2101 (see FIGS. 21A and 21B) is formedin the opening 2001. In some embodiments, the third nanowire 2101 actsas a horizontal portion of the channel of the semiconductor device 1500.

Referring to FIGS. 21A and 21B, the third nanowire 2101 is formed in theopening 2001. In some embodiments, the third nanowire 2101 forms thehorizontal portion of the channel of the semiconductor device 1500. Inthe illustrated embodiment, the channel of the semiconductor device 1500comprises the first nanowire 1801, the second nanowire 1803 and thethird nanowire 2101. In some embodiments, the third nanowire 2101 may beformed using similar material and methods as the third nanowire 901 (seeFIGS. 9A and 9B) and the description is not repeated herein. In someembodiments, the first nanowire 1801, the second nanowire 1803 and thethird nanowire 2101 may comprise a same material. In other embodiments,the first nanowire 1801, the second nanowire 1803 and the third nanowire2101 may comprise different materials.

Referring to FIGS. 22A and 22B, a dielectric layer 2201 is formed overthe dielectric layer 1901. In some embodiments, the dielectric layer2201 may be formed using similar materials and methods as the dielectriclayer 1001 (see FIGS. 10A and 10B) and the description is not repeatedherein. In some embodiments, the dielectric layer 2201 and thedielectric layer 1901 may comprise a same material. In otherembodiments, the dielectric layer 2201 and the dielectric layer 1901 maycomprise different materials.

Referring further to FIGS. 22A and 22B, an opening 2203 is formed from atop surface of the dielectric layer 2201. In some embodiments, theopening 2203 extends through the dielectric layer 2201, the dielectriclayer 1901 and exposes the template layer 1701. Moreover, the opening2203 exposes sidewalls, top and bottom surfaces of the third nanowire2101, and sidewalls and top surfaces of the first nanowire 1801 and thesecond nanowire 1803. In some embodiments, the dielectric layer 2201 andthe dielectric layer 1901 may be patterned using suitable lithographyand etching processes. In some embodiments, the dielectric layers 1901and 2201 may have higher etch selectivities than the template layer 1701and a selective etch process may be used to form the opening 2203. Insome embodiments wherein the dielectric layer 2201 and the dielectriclayer 1901 comprise a same material, the dielectric layer 2201 and thedielectric layer 1901 may be selectively etched using a single etchprocess. In other embodiments wherein the dielectric layer 2201 and thedielectric layer 1901 comprise different materials, the dielectric layer2201 and the dielectric layer 1901 may be selectively etched usingmultiple etch process (for example, two etch processes). As describedbelow in greater detail, a gate stack wrapping the first nanowire 1801,the second nanowire 1803 and the third nanowire 2101 is formed in theopening 2203.

Referring to FIGS. 23A and 23B, a gate stack wrapping the channel(comprising the first nanowire 1801, the second nanowire 1803 and thethird nanowire 2101) of the semiconductor device 1500 is formed in theopening 2203. In some embodiments, a gate dielectric layer 2301 isconformally formed in the opening 2203. In the illustrated embodiment,the gate dielectric layer 2301 covers sidewalls and a bottom of theopening 2203, and exposed surfaces of the first nanowire 1801, thesecond nanowire 11803 and the third nanowire 2101. In some embodiment,the gate dielectric layer 2301 may be formed using similar materials andmethods as the gate dielectric layer 501 (see FIGS. 5A and 5B) and thedescription is not repeated herein. Subsequently, a work function layer2303 is conformally formed in the opening 2203 adjacent the gatedielectric layer 2301. In some embodiment, the work function layer 2303may be formed using similar materials and methods as the work functionlayer 503 (see FIGS. 5A and 5B) and the description is not repeatedherein.

Referring further to FIGS. 23A and 23B, a gate electrode 2305 is formedon exposed surfaces of the work function layer 2303. In someembodiments, the gate dielectric layer 2301 and the work function layer2303 do not completely fill the opening 2203, and the remaining portionof the opening 2203 may be filled by the gate electrode 2305. In someembodiments, the gate electrode 2305 may be formed using similarmaterial and methods as the gate electrode 1105 (see FIGS. 11A and 11B)and the description is not repeated herein. Subsequently, portions ofthe gate dielectric layer 2301, the work function layer 2303 and thegate electrode 2305 extending over the dielectric layer 2201 may beremoved such that top surfaces of the gate dielectric layer 2301, thework function layer 2303 and the gate electrode 2305 are substantiallycoplanar with the top surface of the dielectric layer 2201. In someembodiments, excess materials may be removed using, for example, anetching process, a grinding process, a CMP process, and the like.

Referring to FIGS. 24A and 24B, an ILD layer 2401 is formed over thedielectric layer 2201. In some embodiments, the ILD layer 2401 may beformed using similar materials and methods as the ILD layer 1201 (seeFIGS. 12A and 12B) and the description is not repeated herein.Subsequently, a first contact plug 2403, a second contact plug 2405, anda third contact plug 2407 are formed in the ILD layer 2401 to provideelectrical connections to the first source/drain feature 1503, thesecond source/drain feature 1505 and the gate electrode 2305,respectively. In some embodiments, the first contact plug 2403, thesecond contact plug 2405, and the third contact plug 2407 may be formedusing similar material and methods as the first contact plug 1301, thesecond contact plug 1303, and the third contact plug 1305 (see FIGS. 13Aand 13B), respectively, and the description is not repeated herein. Inthe illustrated embodiment, the first contact plug 2403 extends throughthe ILD layer 2401, the dielectric layer 2201, the dielectric layer1901, and the template layer 1701, and contacts the first source/drainfeature 1503. The second contact plug 2405 extends through the ILD layer2401, the dielectric layer 2201, the dielectric layer 1901, and thetemplate layer 1701, and contacts the second source/drain feature 1505.The third contact plug 2407 extends through the ILD layer 2401 andcontacts the gate electrode 2305.

In some embodiments, further manufacturing steps may be performed on thesemiconductor device 1500. For example, metallization layers (not shown)may be formed over the ILD layer 2401. The metallization layers maycomprise one or more dielectric layers, and one or more conductivefeatures formed in the one or more dielectric layers. In someembodiments, the metallization layers are in electrical contact with thefirst contact plug 2403, the second contact plug 2405, and the thirdcontact plug 2407, and electrically interconnect the semiconductordevice 1500 to other devices formed on the substrate 1501. In someembodiments, the further manufacturing steps may also include formationof one or more redistribution layers (RDLs) over the metallizationlayers, formation of under-bump metallizations (UBMs) over the RLDs, andformation of connectors over the UBMs. Subsequently, the substrate 1501may be singulated into separate dies, which may further undergo variouspackaging processes.

FIG. 25 is a flow diagram illustrating a method 2500 of forming thesemiconductor device 1500 in accordance with some embodiments. Themethod 2500 starts with step 2501, wherein a first source/drain feature(such as first source/drain feature 1503) and a second source/drainfeature (such as the second source/drain feature 1505) are formed on asubstrate (such as the substrate 1501) as described above with referenceto FIGS. 15A-16B. In step 2503, a first nanowire (such as the firstnanowire 1801) and a second nanowire (such as the second nanowire 1803)are formed on the first source/drain feature and the second source/drainfeature, respectively, as described above with reference to FIGS.17A-18B. In some embodiments, the first nanowire and the second nanowireare substantially perpendicular to top surfaces of the firstsource/drain feature and the second source/drain feature. In step 2505,a third nanowire (such as the third nanowire 2101) connecting the firstnanowire to the second nanowire is formed as described with reference toFIGS. 19A-21B. In some embodiments, the third nanowire is substantiallyparallel to the top surfaces of the first source/drain feature and thesecond source/drain feature. In some embodiments, the first nanowire,the second nanowire and the third nanowire form a channel of thesemiconductor device 1500. In step 2507, a gate stack (such as the gatedielectric layer 2301, the work function layer 2303 and the gateelectrode 2305) is formed wrapping around the first nanowire, the secondnanowire and the third nanowire as described above with reference toFIGS. 22A-23B.

FIGS. 26A-33B illustrate various intermediate stages of fabrication of asemiconductor device 2600 in accordance with some embodiments. FIGS.26A-33B illustrate top and cross-sectional views, wherein an “A” figurerepresents a top view and a “B” figure represents a cross-sectional viewalong the B-B′ line of the respective “A” figure. In addition, variouselements of FIGS. 26A-33A are depicted using dashed lines to indicatethat such elements are not visible in the top views illustrated in FIGS.26A-33A. As described above with reference to FIGS. 1A-13B, the channelof the semiconductor device 100 comprises epitaxially grown nanowires(such as the first nanowire 401 and the second nanowire 403). Asdescribed below in greater detail, a channel of the semiconductor device2600 comprises nanowires that are formed using lithography and etchingprocesses.

Referring first to FIGS. 26A and 26B, a portion of a substrate 2601having a feature 2603 formed thereon is illustrated. The substrate 2601may be formed of similar materials as the substrate 101 (see FIGS. 1Aand 1B) and the description is not repeated herein. In some embodiments,the substrate 2601 is patterned to form the feature 2603. In someembodiments, the feature 2603 may be formed using similar methods as thefirst feature 103 and the second feature 105 (see FIGS. 1A and 1B),respectively, and the description is not repeated herein.

Referring to FIGS. 27A and 27B, a semiconductor layer 2701 is formedover the substrate 2601 and the feature 2603. In some embodiments, thesemiconductor layer 2701 may comprise similar candidate materials as thesubstrate 2601 and may be formed using, for example, CVD, LPCVD, ALD,and like. In the illustrated embodiment, the semiconductor layer 2701and the substrate 2601 comprise different materials having differentetch selectivities. As described below in greater detail, the differencebetween the etch selecitivies allows for selective removal of a portionof the substrate 2601. In some embodiments wherein the semiconductorlayer 2701 comprises SiGe, the semiconductor layer 2701 may be formedusing, for example, LPCVD using SiH₄ and GeH₄ as precursor gases. Insome embodiments, the semiconductor layer 2701 has a thickness T₁between about 2 nm and about 200 nm.

As described below in greater detail, the semiconductor layer 2701 ispatterned to form a plurality of channels and source/drain features ofthe semiconductor device 2600. Moreover, lengths of the channels aredetermined by dimensions such as a height and a width of the feature2603. By forming a plurality of features (such as the feature 2603)having different dimensions on a substrate (such as the substrate 2601),it is then possible form semiconductor devices (such the semiconductordevice 2600) having different channel lengths. Furthermore, the featuresof different widths may be formed on the substrate using a singlepatterning process, which advantageously allows for determining channellengths using the single patterning process.

Referring to FIGS. 28A and 28B, the feature 2603 and the semiconductorlayer 2701 are patterned to form fins 2603 a, 2603 b and 2603 c, andcorresponding semiconductor shells 2701 a, 2701 b and 2701 c. In theillustrated embodiment, the semiconductor shells 2701 a, 2701 b and 2701c are disposed on sidewalls and top surfaces of the fins 2603 a, 2603 band 2603 c, respectively. In some embodiments, the feature 2603 and thesemiconductor layer 2701 may be patterned using suitable lithography andetching processes. In the illustrated embodiments, three fins (such asthe fins 2603 a, 2603 b and 2603 c) and the three semiconductor shells(such as the semiconductor shells 2701 a, 2701 b and 2701 c) are formedon the substrate 2601. However, in other embodiments, a number of thefins and the semiconductor shells may be less or more than three basedon design requirements for the semiconductor device 2600. In someembodiments, the semiconductor shells 2701 a, 2701 b and 2701 c haveshapes of nanowires and may be also referred to as nanowires 2701 a,2701 b and 2701 c. As described below in greater detail, thesemiconductor shells 2701 a, 2701 b and 2701 c act as channels of thesemiconductor device 2600. Accordingly, the semiconductor shells 2701 a,2701 b and 2701 c may be also referred to as channels 2701 a, 2701 b and2701 c. In some embodiment, the channels 2701 a, 2701 b and 2701 c havea width W₂ between about 2 nm and about 50 nm.

Referring to FIGS. 29A and 29B, portions of the semiconductor layer 2701on a top surface of the substrate 2601 are patterned to form a firstsource/drain feature 2701 d and a second source/drain feature 2701 e. Insome embodiments, the portions of the semiconductor layer 2701 on thetop surface of the substrate 2601 may be patterned using suitablelithography and etching processes. In the illustrated embodiment, thefirst source/drain feature 2701 d and the second source/drain feature2701 e act as common source/drain features for the channels 2701 a, 2701b and 2701 c.

Referring to FIGS. 30A and 30B, a dielectric layer 3001 is formed overthe substrate 2601, the channels 2701 a, 2701 b and 2701 c, the firstsource/drain feature 2701 d and the second source/drain feature 2701 e.In some embodiments, the dielectric layer 3001 may be formed usingsimilar materials and methods as the dielectric layer 701 (see FIGS. 7Aand 7B) and the description is not repeated herein.

Referring to FIGS. 31A and 31B, the dielectric layer 3001 is patternedto form an opening 3101 in the dielectric layer 3001. In someembodiments, the dielectric layer 3001 may be patterned using suitablelithography and etching processes. In the illustrated embodiment, theopening 3101 exposes the channels 2701 a, 2701 b and 2701 c and the fins2603 a, 2603 b and 2603 c. Subsequently, the fins 2603 a, 2603 b and2603 c are selectively removed such that only the channels 2701 a, 2701b and 2701 c remain in the opening 3101. In some embodiments wherein thefins 2603 a, 2603 b and 2603 c comprise silicon, the fins 2603 a, 2603 band 2603 c may be selectively removed using a wet etch process withetchants such as, for example, tetramethylammonium hydroxide (TMAH),potassium hydroxide (KOH), and the like.

Referring to FIGS. 32A and 32B, a gate stack is formed in the opening3101 and wrapping around the channels 2701 a, 2701 b and 2701 c. In someembodiments, a gate dielectric layer 3201 is conformally formed in theopening 3101. In the illustrated embodiment, the gate dielectric layer3201 covers sidewalls and a bottom of the opening 3101, and exposedsurfaces of the channels 2701 a, 2701 b and 2701 c. In some embodiment,the gate dielectric layer 3201 may be formed using similar materials andmethods as the gate dielectric layer 501 (see FIGS. 5A and 5B) and thedescription is not repeated herein. Subsequently, a work function layer3203 is conformally formed in the opening 3101 adjacent the gatedielectric layer 3201. In some embodiment, the work function layer 3203may be formed using similar materials and methods as the work functionlayer 503 (see FIGS. 5A and 5B) and the description is not repeatedherein.

Referring further to FIGS. 32A and 32B, a gate electrode 3205 is formedon exposed surfaces of the work function layer 3203. In someembodiments, the gate dielectric layer 3201 and the work function layer3203 do not completely fill the opening 3101, and the remaining portionof the opening 3101 may be filled by the gate electrode 3205. In someembodiments, the gate electrode 3205 may be formed using similarmaterial and methods as the gate electrode 1105 (see FIGS. 11A and 11B)and the description is not repeated herein. Subsequently, portions ofthe gate dielectric layer 3201, the work function layer 3203 and thegate electrode 3205 extending over the dielectric layer 3001 may beremoved such that top surfaces of the gate dielectric layer 3201, thework function layer 3203 and the gate electrode 3205 are substantiallycoplanar with the top surface of the dielectric layer 3001. In someembodiments, excess materials may be removed using, for example, anetching process, a grinding process, a CMP process, or the like.

Referring to FIGS. 33A and 33B, an ILD layer 3301 is formed over thedielectric layer 3001. In some embodiments, the ILD layer 3301 may beformed using similar materials and methods as the ILD layer 1201 (seeFIGS. 12A and 12B) and the description is not repeated herein.Subsequently, a first contact plug 3303, a second contact plug 3305, anda third contact plug 3307 are formed in the ILD layer 3301 to provideelectrical connections to the first source/drain feature 2701 d, thesecond source/drain feature 2701 e and the gate electrode 3105,respectively. In some embodiments, the first contact plug 3303, thesecond contact plug 3305, and the third contact plug 3307 may be formedusing similar material and methods as the first contact plug 1301, thesecond contact plug 1303, and the third contact plug 1305 (see FIGS. 13Aand 13B), respectively, and the description is not repeated herein. Inthe illustrated embodiment, the first contact plug 3303 extends throughthe ILD layer 3301, the dielectric layer 3001 and contacts the firstsource/drain feature 2701 d. The second contact plug 3305 extendsthrough the ILD layer 3301, the dielectric layer 3001 and contacts thesecond source/drain feature 2701 e. The third contact plug 3307 extendsthrough the ILD layer 3301 and contacts the gate electrode 3105. In theillustrated embodiment, top-view shapes of the first contact plug 3303,the second contact plug 3305, and the third contact plug 3307 arerectangular shapes. However, in other embodiments, the top-view shapesof the first contact plug 3303, the second contact plug 3305, and thethird contact plug 3307 may be circles, polygons such as triangles,hexagons, and the like.

In some embodiments, further manufacturing steps may be performed on thesemiconductor device 2600. For example, metallization layers (not shown)may be formed over the ILD layer 3301. The metallization layers maycomprise one or more dielectric layers, and one or more conductivefeatures formed in the one or more dielectric layers. In someembodiments, the metallization layers are in electrical contact with thefirst contact plug 3303, the second contact plug 3305, and the thirdcontact plug 3307, and electrically interconnect the semiconductordevice 2600 to other devices formed on the substrate 2601. In someembodiments, the further manufacturing steps may also include formationof one or more redistribution layers (RDLs) over the metallizationlayers, formation of under-bump metallizations (UBMs) over the RLDs, andformation of connectors over the UBMs. Subsequently, the substrate 2601may be singulated into separate dies, which may further undergo variouspackaging processes.

FIG. 34 is a flow diagram illustrating a method 3400 of forming thesemiconductor device 2600 in accordance with some embodiments. Themethod 3400 starts with step 3401, wherein a feature (such as thefeature 2603) is formed on a substrate (such as the substrate) asdescribed above with reference to FIGS. 26A and 26B. In step 3403, asemiconductor layer (such as the semiconductor layer 2701) is formed ona top surface and sidewalls of the feature as described above withreference to FIGS. 27A and 27B. In step 3405, the semiconductor layer ispatterned to form a first source/drain feature (such as the firstsource/drain feature 2701 d), a second source/drain feature (such as thesecond source/drain feature 2701 e) and a plurality of channels (such asthe channels 2701 a, 2701 b and 2701 c) extending from the firstsource/drain feature to the second source/drain feature as describedabove with reference to FIGS. 28A-29B. In step 3407, the feature isremoved to expose the plurality of channels as described above withreference to FIGS. 30A-31B. In step 3409, a gate stack (such as the gatedielectric layer 3201, the work function layer 3203 and the gateelectrode 3205) is formed wrapping around the plurality of channels asdescribed above with reference to FIGS. 32A-32B.

FIGS. 35A-42B illustrate various intermediate stages of fabrication of asemiconductor device 3500 in accordance with some embodiments. FIGS.35A-42B illustrate top and cross-sectional views, wherein an “A” figurerepresents a top view and a “B” figure represents a cross-sectional viewalong the B-B′ line of the respective “A” figure. In addition, variouselements of FIGS. 35A-42A are depicted using dashed lines to indicatethat such elements are not visible in the top views illustrated in FIGS.35A-42A. As described above with reference to FIGS. 1A-13B, the channelof the semiconductor device 100 comprises the first nanowire 401 and thesecond nanowire 403 extending vertically from the uppermost surfaces ofthe first source/drain feature 103 and the second source/drain feature105, respectively, and the third nanowire 901 connecting top portions ofthe first nanowire 401 and the second nanowire 403. As described belowin greater detail, a channel of the semiconductor device 2600 comprisesa fin formed on a substrate, and nanowires extending vertically fromopposite ends of the fin.

Referring first to FIGS. 35A and 35B, a portion of a substrate 3501having a fin 3503 formed thereon is illustrated. The substrate 3501 maybe formed of similar materials as the substrate 101 (see FIGS. 1A and1B) and the description is not repeated herein. In some embodiments, thesubstrate 3501 is patterned to form the fin 3503. In some embodiments,the fin 3503 may be formed using similar methods as the first feature103 and the second feature 105 (see FIGS. 1A and 1B) and the descriptionis not repeated herein.

As described below in greater detail, the fin 3503 acts as a horizontalportion of a channel of the semiconductor device 3500. Accordingly, alength of the channel depends on a length of the fin 3503. By forming aplurality of fins (such as the fin 3503) having different lengths on asubstrate (such as the substrate 3501), it is then possible to formsemiconductor devices (such as the semiconductor devices 3500) havingdifferent channel lengths. Furthermore, the fins of different lengthsmay be formed on the substrate using a single patterning process, whichadvantageously allows for determining channel lengths using the singlepatterning process.

Referring to FIGS. 36A and 36B, an STI structure 3601 is formed over thesubstrate 3501 and on sidewalls of the fin 3503. In some embodiments,the STI structure 3601 may be formed using similar material and methodsas the STI structure 201 (see FIGS. 2A and 2B) and the description isnot repeated herein. Subsequently, a template layer 3603 is formed overthe STI structure 3601 and the fin 3503. In some embodiments, thetemplate layer 3603 may be formed using similar materials and methods asthe template layer 301 (see FIGS. 3A and 3B) and the description is notrepeated herein.

Referring further to FIGS. 36A and 36B, the template layer 3603 ispatterned form a first opening 3605 and a second opening 3607 therein.In some embodiments, the first opening 3605 and the second opening 3607expose respective ends of the fin 3503. In some embodiments, the firstopening 3605 and the second opening 3607 may be formed using similarmethods as the first opening 303 and the second opening 305 (see FIGS.3A and 3B) and the description is not repeated herein.

Referring to FIGS. 37A and 37B, a first nanowire 3701 and a secondnanowire 3703 are formed in the first opening 3605 and the secondopening 3607 (see FIGS. 36A and 36B), respectively. As described belowin greater detail, the first nanowire 3701 and the second nanowire 3703form vertical portions of the channel of the semiconductor device 3500.In some embodiments, the first nanowires 3701 and the second nanowires3703 may be formed using similar material and methods as the firstnanowire 401 and the second nanowire 403 (see FIGS. 4A and 4B) and thedescription is not repeated herein. In the illustrated embodiment, thefin 3503, the first nanowire 3701 and the second nanowire 3703 form thechannel of the semiconductor device 3500.

Referring to FIGS. 38A and 38B, a dielectric layer 3801 is formed overthe template layer 3603 and surrounding the first nanowire 3701 and thesecond nanowire 3703. In some embodiments, the dielectric layer 3801 maybe formed using similar materials and methods as the dielectric layer701 (see FIGS. 7A and 7B) and the description is not repeated herein.

Referring to FIGS. 39A and 39B, the dielectric layer 3801, the templatelayer 3603 and the STI structure 3601 are recessed to form an opening3901. In some embodiments, the opening 3901 may be formed using suitablelithography and etching processes. In the illustrated embodiment, theopening 3901 exposes a top surface and sidewalls of the fin 3503, andtop surfaces and sidewalls of the first nanowire 3701 and the secondnanowire 3703. In some embodiments, the dielectric layer 3801, thetemplate layer 3603 and the STI structure 3601 may have higher etchselectivities than the fin 3503 and a selective etch process may be usedto form the opening 3901. As described below in greater detail, a gatestack wrapping the channel of the semiconductor device 3500 is formed inthe opening 3901.

Referring to FIGS. 40A and 40B, a gate stack wrapping the channel(comprising the first nanowire 3701, the second nanowire 3703 and thefin 3503) of the semiconductor device 3500 is formed in the opening3901. In some embodiments, a gate dielectric layer 4001 is conformallyformed in the opening 3901. The gate dielectric layer 4001 coverssidewalls and a bottom of the opening 3901, and exposed surfaces of thefirst nanowire 3701, the second nanowire 3703 and the fin 3503. In someembodiment, the gate dielectric layer 4001 may be formed using similarmaterials and methods as the gate dielectric layer 501 (see FIGS. 5A and5B) and the description is not repeated herein. Subsequently, a workfunction layer 4003 is conformally formed in the opening 3901 adjacentthe gate dielectric layer 4001. In some embodiment, the work functionlayer 4003 may be formed using similar materials and methods as the workfunction layer 503 (see FIGS. 5A and 5B) and the description is notrepeated herein.

Referring to FIGS. 41A and 41B, a dielectric layer 4101 is formed in theopening 3901. In some embodiments, the dielectric layer 4101 may beformed using similar materials and methods as the dielectric layer 701(see FIGS. 7A and 7B) and the description is not repeated herein. Insome embodiments, the dielectric layer 3801 and the dielectric layer4101 are formed of a same material. In other embodiments, the dielectriclayer 3801 and the dielectric layer 4101 are formed of differentmaterials. Subsequently, portions of the gate dielectric layer 4001, thework function layer 4003 and the dielectric layer 4101 extending overthe dielectric layer 3801 may be removed such that top surfaces of thegate dielectric layer 4001, the work function layer 4003 and thedielectric layer 4101 are substantially coplanar with a top surface ofthe dielectric layer 3801. In some embodiments, excess materials may beremoved using, for example, an etching process, a grinding process, aCMP process, and the like.

Referring to FIGS. 42A and 42B, an ILD layer 4201 is formed over thedielectric layer 3801. In some embodiments, the ILD layer 4201 may beformed using similar materials and methods as the ILD layer 1201 (seeFIGS. 12A and 12B) and the description is not repeated herein.Subsequently, a first contact plug 4203, a second contact plug 4205, anda third contact plug 4207 are formed in the ILD layer 4201 to provideelectrical connections to the first nanowire 3701, the second nanowire3703 and the work function layer 4003, respectively. In someembodiments, the first contact plug 4203, the second contact plug 4205,and the third contact plug 4207 may be formed using similar material andmethods as the first contact plug 1301, the second contact plug 1303,and the third contact plug 1305 (see FIGS. 13A and 13B), respectively,and the description is not repeated herein. In the illustratedembodiment, the first contact plug 4203 extends through the ILD layer4201 and contacts the first nanowire 3701. The second contact plug 4205extends through the ILD layer 4201 and contacts the second nanowires3703. The third contact plug 4207 extends through the ILD layer 4201 andcontacts the work function layer 4003.

Referring further to FIGS. 42A and 42B, in the illustrated embodiment,the third contact plug 4207 directly contacts the work function layer4003. In other embodiments, before filling the opening 3901 with thedielectric layer 4101, a gate electrode (not shown) may be formed in theopening 3901. In some embodiments, the gate electrode may be formedusing similar materials and methods as the gate electrode 1105 (seeFIGS. 11A and 11B) and the description is not repeated herein. In someembodiments, the gate electrode may partially or fully fill the opening3901.

In some embodiments, further manufacturing steps may be performed on thesemiconductor device 3500. For example, metallization layers (not shown)may be formed over the ILD layer 4201. The metallization layers maycomprise one or more dielectric layers, and one or more conductivefeatures formed in the one or more dielectric layers. In someembodiments, the metallization layers are in electrical contact with thefirst contact plug 4203, the second contact plug 4205, and the thirdcontact plug 4207, and electrically interconnect the semiconductordevice 3500 to other devices formed on the substrate 3501. In someembodiments, the further manufacturing steps may also include formationof one or more redistribution layers (RDLs) over the metallizationlayers, formation of under-bump metallizations (UBMs) over the RLDs, andformation of connectors over the UBMs. Subsequently, the substrate 3501may be singulated into separate dies, which may further undergo variouspackaging processes.

FIG. 43 is a flow diagram illustrating a method 4300 of forming thesemiconductor device 3500 in accordance with some embodiments. Themethod 4300 starts with step 4301, wherein a fin (such as the fin 3503)is formed on a substrate (such as the substrate 3501) as described abovewith reference to FIGS. 35A and 35B. In step 4303, a first nanowire(such as the first nanowire 3701) and a second nanowire (such as thesecond nanowire 3703) are formed on opposite ends of the fin asdescribed above with reference to FIGS. 36A-37B. In some embodiments,the first nanowire, the second nanowire and the fin form a channel ofthe semiconductor device 3500. In step 4305, a gate stack (such as thegate dielectric layer 4001 and the work function layer 4003) is formedwrapping around the first nanowire, the second nanowire and the fin asdescribed above with reference to FIGS. 38A-40B.

According to an embodiment, a semiconductor device includes a substrate,the substrate having a first source/drain feature and a secondsource/drain feature formed thereon, and a first nanowire on the firstsource/drain feature, the first nanowire extending vertically from anupper surface of the first source/drain feature. The semiconductordevice further includes a second nanowire on the second source/drainfeature, the second nanowire extending vertically from an upper surfaceof the second source/drain feature, and a third nanowire extending froman upper end of the first nanowire to an upper end of the secondnanowire, wherein the first nanowire, the second nanowire and the thirdnanowire form a channel.

According to another embodiment, a semiconductor device includes a finextending from a substrate, and a first nanowire on a first end of thefin, the first nanowire extending vertically from an upper surface ofthe fin. The semiconductor device further includes a second nanowire ona second end of the fin, the second nanowire extending vertically fromthe upper surface of the fin, wherein the first nanowire, the secondnanowire and the fin form a channel of a transistor.

According to yet another embodiment, a method of forming a semiconductordevice, the method includes forming a first source/drain feature and asecond source/drain feature on a substrate, forming a first dielectriclayer on the first source/drain feature and the second source/drainfeature, and patterning the first dielectric layer to form a firstopening and a second opening therein, the first opening exposing thefirst source/drain feature and the second opening exposing the secondsource/drain feature. The method further includes epitaxially growing afirst nanowire in the first opening and a second nanowire in the secondopening, the first nanowire extending vertically from an upper surfaceof the first source/drain feature and the second nanowire extendingvertically from an upper surface of the second source/drain feature, andforming a second dielectric layer on the first dielectric layer andsurrounding the first nanowire and the second nanowire. The methodfurther includes patterning the second dielectric layer to form a thirdopening therein, the third opening exposing at least a portion of thefirst nanowire and at least a portion of the second nanowire, andforming a third nanowire in the third opening, the third nanowireextending form an upper end of the first nanowire to an upper end of thesecond nanowire.

According to yet another embodiment, a semiconductor device includes afin extending from a substrate, and a first nanowire on a first end ofthe fin, the first nanowire extending vertically from an upper surfaceof the fin. The semiconductor device further includes a second nanowireon a second end of the fin, the second nanowire extending verticallyfrom the upper surface of the fin, wherein at least a portion of thefirst nanowire, at least a portion of the second nanowire and the finform a channel of a transistor.

According to yet another embodiment, a semiconductor device includes asubstrate, the substrate having a plurality of recesses, a firstsource/drain feature interposed between a first pair of adjacentrecesses, and a second source/drain feature interposed between a secondpair of adjacent recesses. The semiconductor device further includes afirst nanowire physically contacting a first upper surface of the firstsource/drain feature, the first nanowire extending vertically from thefirst upper surface of the first source/drain feature, a second nanowirephysically contacting a second upper surface of the second source/drainfeature, the second nanowire extending vertically from the second uppersurface of the second source/drain feature, and a third nanowireextending between a first sidewall of the first nanowire and a secondsidewall of the second nanowire, wherein the first nanowire, the secondnanowire and the third nanowire form a channel.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A semiconductor device comprising: a substrate, the substrate having a first source/drain feature and a second source/drain feature formed thereon; a first nanowire on the first source/drain feature, the first nanowire extending vertically from an upper surface of the first source/drain feature; a second nanowire on the second source/drain feature, the second nanowire extending vertically from an upper surface of the second source/drain feature; and a third nanowire extending from an upper end of the first nanowire to an upper end of the second nanowire, wherein the first nanowire, the second nanowire and the third nanowire form a channel.
 2. The semiconductor device of claim 1, further comprising a gate stack wrapped around the channel.
 3. The semiconductor device of claim 1, wherein the upper surface of the first source/drain feature is substantially coplanar with the upper surface of the second source/drain feature.
 4. The semiconductor device of claim 1, wherein the first nanowire and the second nanowire comprise a first material, and wherein the third nanowire comprises a second material, the second material being different from the first material.
 5. The semiconductor device of claim 1, wherein the first nanowire, the second nanowire and the third nanowire comprise a same material.
 6. The semiconductor device of claim 1, further comprising a dielectric layer over the first source/drain feature and the second source/drain feature, the first nanowire and the second nanowire extending through the dielectric layer and contacting the first source/drain feature and the second source/drain feature, respectively.
 7. The semiconductor device of claim 1, further comprising a shallow trench isolation (STI) structure, the STI structure being interposed between the first source/drain feature and the second source/drain feature.
 8. A semiconductor device comprising: a substrate, the substrate having a plurality of recesses; a first source/drain feature interposed between a first pair of adjacent recesses; a second source/drain feature interposed between a second pair of adjacent recesses; a first nanowire physically contacting a first upper surface of the first source/drain feature, the first nanowire extending vertically from the first upper surface of the first source/drain feature; a second nanowire physically contacting a second upper surface of the second source/drain feature, the second nanowire extending vertically from the second upper surface of the second source/drain feature; and a third nanowire extending between a first sidewall of the first nanowire and a second sidewall of the second nanowire, wherein the first nanowire, the second nanowire and the third nanowire form a channel.
 9. The semiconductor device of claim 8, wherein a first upper end of the first nanowire extends through the third nanowire.
 10. The semiconductor device of claim 9, wherein a second upper end of the second nanowire extends through the third nanowire.
 11. The semiconductor device of claim 8, wherein the first nanowire and the second nanowire comprise a III-V compound semiconductor material.
 12. The semiconductor device of claim 8, further comprising a gate stack extending along the first sidewall of the first nanowire and the second sidewall of the second nanowire.
 13. The semiconductor device of claim 8, wherein a third width of the third nanowire is greater than a first width of the first nanowire and a second width of the second nanowire.
 14. A structure comprising: a substrate, the substrate having a first source/drain feature and a second source/drain feature, the first source/drain feature being separated from the second source/drain feature by a shallow trench isolation (STI) structure; a first dielectric layer on the first source/drain feature and the second source/drain feature; a first nanowire formed through the first dielectric layer and extending above the first dielectric layer, the first nanowire coupled to the first source/drain feature; a second nanowire formed through the first dielectric layer and extending above the first dielectric layer, the second nanowire coupled to the second source/drain feature; a second dielectric layer on the first dielectric layer, the second dielectric layer having a top surface that is substantially coplanar with a top of the first nanowire and a top of the second nanowire, wherein the first nanowire and second nanowire are encompassed by the second dielectric layer except for a top portion of the first nanowire and a top portion of the second nanowire; and a third nanowire coupling the top portion of the first nanowire and the top portion of the second nanowire, the third nanowire having a top surface that is substantially coplanar with the top surface of the second dielectric layer.
 15. The structure of claim 14, wherein the first nanowire, second nanowire, and third nanowire form a channel, and the structure further comprises a gate stack wrapped around the channel.
 16. The structure of claim 14, wherein the third nanowire extends laterally beyond the first nanowire and laterally beyond the second nanowire.
 17. The structure of claim 14, further comprising a gate dielectric over the third nanowire and a gate electrode on the gate dielectric.
 18. The structure of claim 17, further comprising a third dielectric layer on the second dielectric layer, wherein the gate dielectric is formed within an opening in the third dielectric layer.
 19. The structure of claim 15, wherein the gate stack comprises a gate dielectric layer and a work function layer.
 20. The structure of claim 15, wherein the gate stack is formed between the first nanowire and the second nanowire on the first dielectric layer. 